The invention relates to a calendar mechanism, especially of a modular structure, which can be mounted in clock mechanisms, especially in the form of a perpetual calendar which is actuated via a wheel of a clock, which wheel performs a revolution in 24 hours, the display being effected separated into units and tens via a printed display disc, which is provided with a toothing, and a programme carrier being provided which performs a revolution in 31 days.
Calendar mechanisms of this type are known with various structures, the date mechanism or date movement being moved on at very low speed via levers and ratchets. In such a mechanism, both daily movement steps and also movement steps covering a plurality of days (from the 30th over the 31st to the 1st in xe2x80x9cshortxe2x80x9d months and from the 28.02 or 29.02 to 01.03) must be produced, which is normally effected via gears with intermittent movement.
For the purpose of adjusting the calendar or for general correction of all the displays, a manual correction button is used which is accessible from outside, said button acting upon the date mechanism via the same levers and ratchets which effect shifting at relatively slow speed in normal operation.
The speeds acting on the mechanism during manual correction diverge individually very greatly. They can achieve dimensions where the catch springs available per se no longer ensure safe stopping of the display discs due to their inertia which is significantly greater in comparison to normal hands so that the result is over-rotation of the display elements.
In order to deal with this problem, one could configure the catch springs, which fix the end position of the movement, with increased elastic force, as a result of which however the torque loading of the clock mechanism increases greatly so that the duration of the action and the precision of the action drop considerably.
Proceeding from here, the object underlying the invention is to configure a date mechanism of the type mentioned initially in such a manner that over-rotation is prevented without the duration and precision of the action being substantially affected.
This object is achieved according to the invention in that the programme carrier actuates additional locking elements in such a manner that, on those days on which the risk of over-rotation exists, they are swung in and out again in the rotational movement of the display discs and correspondingly prevent over-rotation in cooperation with the toothing of the display discs.
According to the invention, the risk of over-rotation by the programme carrier is therefore prevented in that when and only when the corresponding risk exists, an additional locking is provided. On the remaining days, the locking elements do not act upon the date mechanism or the clock mechanism so that the function of the clock mechanism remains completely unaffected other than in the case of an increase in the elastic force of the catch springs.
It can be provided thereby that additional control elements are fitted on the programme carrier or the control elements are produced by the configuration of the programme carrier, the control elements respectively actuating the locking elements.
It is provided in a further embodiment of the invention that the additional locking element is a ratchet which can be pivoted about a pivot bearing axis, said ratchet being retained out of engagement relative to the toothing of the display disc by means of a spring in the non-locking period of time.
It is provided in another embodiment according to the invention that one of the catch springs carries a pin as locking element which cooperates with the programme carrier, and the bending point of which springs is positioned such that the pin describes a track which enables a locking and detaching function.